Abrasive particles having a unique morphology

ABSTRACT

An abrasive particle having an irregular surface, wherein the surface roughness of the particle is less than about 0.95. A method for producing modified abrasive particles, including providing a plurality of abrasive particles, providing a reactive coating on said particles, heating said coated particles; and recovering modified abrasive particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional patent application Ser. No.12/560,899 filed Sep. 16, 2009, which claims priority to U.S.provisional patent application No. 61/097,422 filed Sep. 16, 2008, andU.S. Provisional Patent Application Ser. No. 61/187,789, filed Jun. 17,2009. The present application relates to pending patent application Ser.No. 12/560,923 filed on Sep. 16, 2009, patent application Ser. No.12/560,960, filed on Sep. 16, 2009, now granted U.S. Pat. No. 8,182,562,pending patent application Ser. No. 13/362,017, filed Jan. 31, 2012,pending continue-in-part application Ser. No. 13/289,255, filed Nov. 4,2011.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY

The present invention relates to abrasive particles having a uniquemorphology. More particularly, the invention relates to roughening thesurface of diamond particles to enhance their performance in industrialapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F are scanning electron microscope (SEM) images ofconventional monocrystalline diamond, modified diamond using a nickelcoating process and diamond modified using an iron powder process.

FIG. 2 is a Table 1 showing the physical characteristics and performanceof 4-8 μm diamond particles, e.g. powders, before and aftermodification.

FIG. 3 is a graph that shows the surface roughness distribution ofconventional diamond powder, modified diamond powder using a nickelcoating process and a diamond powder modified using an iron powderprocess.

FIG. 4 is a graph that shows the sphericity distribution of conventionaldiamond powder, modified diamond powder using a nickel coating processand a diamond powder modified using an iron powder process.

FIG. 5 is a graph showing the material removal rate and resultingsurface finish of sapphire wafers from a lapping process using slurriesmade from various diamond powders including modified diamond powderusing a nickel coating process.

FIGS. 6A and 6B are comparative drawings of conventional diamondparticle (6A) and a modified diamond particle (6B).

FIG. 7 is an SEM image of a conventional diamond particle.

FIG. 8 is an SEM image of a modified diamond particle using a nickelcoating process.

FIG. 9A-9D are scanning electron microscope (SEM) images of the diamondparticles of an embodiment.

FIGS. 10A-10D are scanning electron microscope (SEM) images of thediamond particles of an embodiment.

FIGS. 11A-11D are scanning electron microscope (SEM) images of thediamond particles of an embodiment.

FIG. 12 is a scanning electron microscope (SEM) image of conventionalmonocrystalline diamond particles.

FIG. 13 shows Table 1 describing characteristics and performance of thediamond particles of an embodiment.

FIG. 14 is a graph depicting characteristics and performance of thediamond particles of an embodiment.

FIG. 15 is a graph showing the characteristics of the diamond particlesof an embodiment.

FIG. 16 is a scanning electron microscope (SEM) image of a diamondparticle of an embodiment.

FIG. 17 is a scanning electron microscope (SEM) image of a diamondparticle of an embodiment.

FIG. 18 is a scanning electron microscope (SEM) image of a diamondparticle of an embodiment.

FIG. 19 is a scanning electron microscope (SEM) image of a diamondparticle of an embodiment.

FIG. 20 is a scanning electron microscope (SEM) image of a diamondparticle of an embodiment.

FIG. 21 is a scanning electron microscope (SEM) image of a diamondparticle of an embodiment.

FIG. 22 is a graph comparing the lapping performance of conventionalmonocrystalline diamond particles, conventional polycrystalline diamondparticles and the monocrystalline diamond particles of an embodiment.

FIG. 23 shows Table 2 containing experimental conditions.

FIG. 24 is an illustration supplementing the “Definitions” section.

FIG. 25 is an illustration supplementing the “Definitions” section.

FIG. 26 is an illustration supplementing the “Definitions” section.

FIGS. 27A and 27B are SEM images of diamond particles of an embodiment.

DETAILED DESCRIPTION

Before the present methods, systems and materials are described, it isto be understood that this disclosure is not limited to the particularmethodologies, systems and materials described, as these may vary. It isalso to be understood that the terminology used in the description isfor the purpose of describing the particular versions or embodimentsonly, and is not intended to limit the scope. For example, as usedherein and in the appended claims, the singular forms “a,” “an,” and“the” include plural references unless the context clearly dictatesotherwise. In addition, the word “comprising” as used herein is intendedto mean “including but not limited to.” Unless defined otherwise, alltechnical and scientific terms used herein have the same meanings ascommonly understood by one of ordinary skill in the art.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as size, weight, reaction conditions and soforth used in the specification and claims are to the understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties sought to be obtained by theinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

As used herein, the term “about” means plus or minus 10% of thenumerical value of the number with which it is being used. Therefore,about 50% means in the range of 45%-55%.

Definitions

In describing and claiming the invention, the following terminology willbe used in accordance with the definitions set forth below.

The term “abrasive”, as used herein, refers to any material used to wearaway softer material.

The term “material removal”, as used herein, refers to the weight of aworkpiece removed in a given period of time reported in milligrams,grams, etc.

The term, “material removal rate”, as used herein, refers to materialremoved divided by the time interval reported as milligrams per minute,grams per hour, etc.

The term “mono crystalline diamond”, as used herein, refers to diamondthat is formed either by high-pressure/high-temperature synthesis or adiamond that is naturally formed. Fracture of monocrystalline diamondproceeds along atomic cleavage planes. A monocrystalline diamondparticle breaks relatively easily at the cleavage planes.

The term “particle” or “particles”, as used herein, refers to a discretebody or bodies. A particle is also considered a crystal or a grain.

The term “pit”, as used herein, refers to an indentation or crevice inthe particle, either an indentation or crevice in the two-dimensionalimage or an indentation or crevice in an object.

The term “polycrystalline diamond”, as used herein, refers to diamondformed by explosion synthesis resulting in a polycrystalline particlestructure. Each polycrystalline diamond particle consists of largenumbers of microcrystallites less than about 100 angstroms in size.Polycrystalline diamond particles do not have cleavage planes.

The term “spike”, as used herein, refers to a sharp projection pointingoutward from the centroid of a particle, a sharp projection pointingoutward from the centroid of a two-dimensional image or a sharpprojection pointing outward from an object.

The term “superabrasive”, as used herein, refers to an abrasivepossessing superior hardness and abrasion resistance. Diamond and cubicboron nitride are examples of superabrasives and have Knoop indentationhardness values of over 3500.

The term “weight loss”, as used herein, refers to the difference inweight of a group of particles before being subject to the modificationtreatment and the weight of the same mass of diamond particles orabrasive particles after being subjected to the modification treatment.

The term “workpiece”, as used herein, refers to parts or objects fromwhich material is removed by grinding, polishing, lapping or othermaterial removal methods.

The term “perimeter”, as used herein, refers to the boundary of a closedplane figure or the sum of all borders of a two-dimensional image.

The term “convex perimeter”, as used herein, refers to a line joiningFeret tangent points, where Feret is the distance between two paralleltangents touching the boundary on each side of a two dimensional imageor object. FIGS. 24-26 provide illustrations of these concepts.

The term “surface roughness”, as used herein, refers to the measurementof a two-dimensional image that quantifies the extent or degree of pitsand spikes of an object's edges or boundaries as stated in the CLEMEXimage analyzer, Clemex Vision User's Guide PE 3.5 ©2001. Surfaceroughness is determined by the ratio of the convex perimeter divided bythe perimeter.

$\begin{matrix}{{{Surface}\mspace{14mu}{Roughness}} = \frac{ConvexPerimeter}{Perimeter}} & {i.}\end{matrix}$

Note that as the degree of pits and spikes increases, the surfaceroughness factor decreases.

The term “sphericity”, as used herein, refers to the estimate of theenclosed area of a two dimensional image or object (4πA) divided by thesquare of perimeter (p²).

$\begin{matrix}{{Sphericity} = \frac{4\pi\; A}{p^{2}}} & {i.}\end{matrix}$

The term “surface area” as used herein, refers to the external surfaceof a particle. When used with a plurality of particles, i.e., powder,the term specific surface area is used and is reported as surface areaper gram of powder.

The term “wafer roughness” when referring to the surface of the sapphireare the features on the surface of the wafer. These features, whichinclude the fine scratches or track marks from abrasive polishing, aremeasured using a contact or non-contact profilometer.

The terms diamond particle or particles and diamond powder or powdersare used synonymously in the instant application and have the samemeaning as “particle” defined above.

It is important to note that although the terms defined above refer tomeasuring two-dimensional particle profiles using microscopic measuringtechniques, it is understood that the features extend to thethree-dimensional form. Automated image analysis of particle size andshape is recognized by one skilled in the art as a reliable,reproducible method of measuring particle characteristics. Although theCLEMEX image analyzer was used, similar devices are available that willreproduce the data.

In one embodiment, monocrystalline diamond particles may be used.Monocrystalline diamond particles in sizes of less than about 100microns are useful. However, diamond particles in sizes over about 100microns may be used as well. The sizes of the diamond particles rangefrom about 0.1 to about 1000 microns. One example of diamond particlesthat may be used is SJK-5 4-8 micron, synthetic industrial diamondparticles manufactured by Diamond Innovations, Inc. (Worthington, Ohio,U.S.A).

In another embodiment, natural diamond particles, sinteredpolycrystalline diamond or shock synthesized polycrystalline diamondparticles may be subjected to the modification treatment discussedbelow.

In an embodiment, other abrasives may be subjected to a modificationtreatment. Examples of abrasives include any material, such as minerals,that are used for shaping or finishing a workpiece. Superabrasivematerials such as natural and synthetic diamond and boron, carbon andnitrogen compounds may be used. Suitable diamond materials may becrystalline or polycrystalline. Other examples of abrasive grains mayinclude calcium carbonate, emery, novaculite, pumice dust, rouge, sand,ceramics, alumina, glass, silica, silicon carbide, and zirconia alumina.

In another embodiment, a reactive coating is used to modify the abrasiveor superabrasive particles. Such reactive coatings include but are notlimited to alkali metal hydroxides, such as lithium hydroxide, sodiumhydroxide, potassium hydroxide, potassium carbonate, sodium peroxide,potassium dichromate and potassium nitrate, etc. The reactive coatingsmay also include a combination of alkali metal hydroxides.

Still other examples of metals that may be utilized as the reactivecoating are those included in Group VIII of the Periodic table, theirmetal compounds and combinations thereof. Other examples of materialthat may be used as reactive coatings include the catalyst metals taughtin U.S. Pat. No. 2,947,609 and the catalyst metals taught in U.S. Pat.No. 2,947,610.

In an embodiment, a metal coating is used as the reactive coating andthe abrasive material is diamond. The weight ratio of diamond particlesto the metal coating is about 10 wt % to about 90 wt % Ni or about 10 wt% to about 60 wt % Ni. However, it should be noted that these ratios area matter of economic efficiency rather than technical effectiveness. Inone embodiment, the metal coating at least partially covers the diamondparticles. Alternatively, the metal coating may uniformly surround eachdiamond particle. It is not necessary that the metal be chemicallybonded to the diamond. Nickel and/or nickel alloys may be used as acoating for the diamond. A method of application of the nickel to thediamond is with an electroless deposition process however methods suchas electrolytic plating, physical vapor deposition or chemical vapordeposition may be used to coat the diamond particles with a layer ofnickel.

In an embodiment, diamond particles are coated with from about 10 toabout 60 weight percent nickel phosphorous coating. The coating processinitially subjects the uncoated diamond particles to a solution ofcolloidal palladium. The fine palladium particles uniformly adsorb ontothe surface of the diamond making the surface autocatalytic forelectroless deposition of nickel. In the next stage of the process, theactivated diamond is placed into nickel sulfamate solution containingabout 10 grams per liter dissolved nickel. While the activated diamondand nickel suspension is mixing, sodium hypophosphate is added to thesuspension and the temperature of the coating bath is maintained atabout 80 degrees C. When the hypophosphate solution is added, all of thedissolved nickel in solution will autocatalytically deposit onto theactivated diamond surfaces.

Depending on how much nickel deposits onto the diamond, more nickel maybe added by replacing the spent nickel/hypophosphate solution with freshsolutions and repeating the process. If uniformly coating the particle,several cycles may be required to obtain a sufficiently uniform coverageof nickel over each of the diamond particles. By monitoring the numberof cycles and controlling the coating bath parameters like temperature,pH and mixing energy, the nickel content on the diamond is veryreproducible. It is not uncommon for the coated diamond to have somelevel of agglomerations as a consequence of the interactions of thediamond particles and nickel plating during the coating. So long as theindividual particles that comprise the agglomerates contain some amountof nickel coating, the presence of agglomerates does not affect thequality of the process and no attempt at removing agglomerates isrequired.

After the diamond particles have been coated, the coated particles areplaced into a furnace and, in a hydrogen atmosphere, vacuum atmosphere,or an inert gas atmosphere, heated from about 650° C. to about 1000° C.Temperatures of about 700° C. to about 950° C. or about 800° C. to about900° C. may be used. The coated diamond may be heated for a period oftime of from about five minutes up to about five hours. Time periodsranging from about thirty minutes up to about two hours or of about oneto about two hours may be used.

After the heating cycle is complete and the particles are cooled, themodified diamond particles are recovered by dissolving the nickel coateddiamond in common acids. Acids that may be used include hydrochloricacid, hydrofluoric acids, nitric acid and certain combinations thereof.Acids, or combinations thereof, are added in an acid-to-coated-diamondratio of 100:1 up to 1000:1 (by volume). The mixture is then heatedbetween about 100° C. to about 120 C.° for a period of from about six toabout eight hours. The solution is then cooled, the liberated diamondsettles and the solution is decanted. The acid cleaning and heatingsteps are repeated until substantially all of the metal coating has beendigested.

Subsequently, any converted graphite (carbon from diamond that has beenconverted to graphite during the reaction with nickel) is then removedfrom the diamond particles via any dissolution treatment method known inthe art. An example of a common dissolution procedure includes theoxidation of graphitic carbons by gradual heating range between about150° C. to about 180° C. in an acidic solution containing a mixture ofHNO₃ and H₂SO₄.

Depending on the furnace conditions chosen, more or less reaction mayoccur between the metal and the diamond. The more the metal etches intothe diamond, the more graphite is formed and, thus, more weight is lostby the diamond. To completely dissolve the graphite, higher quantitiesof acid may be used or additional dissolution treatments may benecessary. The diamond particles are then washed to remove acids andresidue, such as in water. Subsequently, the diamond particles are driedin an oven, air dried, subjected to microwave drying or other dryingmethods known in the art.

One embodiment pertains to monocrystalline diamond particles having veryrough, irregular surfaces as shown in FIGS. 1C and 1D. FIG. 1D shows apopulation of diamond particles and FIG. 1C shows an enlargement of aparticle from FIG. 1D. The particles have been modified using the methoddescribed above. In addition to the roughened appearance, the modifieddiamond particles have unique characteristics as compared toconventional monocrystalline diamond particles shown in FIGS. 1A and 1B.FIG. 1B shows a population of monocrystalline diamond particles and FIG.1A shows an enlargement of a particle from FIG. 1B. The conventionalmonocrystalline diamond particles produced by milling were not subjectedto the modification treatment.

As shown in FIG. 1D, the modified diamond particles includesignificantly more spikes and pits than conventional monocrystallinediamond shown in FIG. 1A. The spikes act as cutting edges when used infree-abrasive slurry applications. It has been discovered that theperformance of the diamond particles of the instant applicationsignificantly improves when used in free abrasive lapping applicationswithin a liquid slurry or suspension. When the modified diamondparticles are used in a fixed bond system, the pits and the spikes helpsecure the particle within the bond system.

In an embodiment, metal particles are used to modify the diamondparticles. The weight ratio of diamond particles to metal particles is1:5 to 5:1. However, it should be noted that these ratios are a matterof economic efficiency rather than technical effectiveness. The size ofthe metal particles is in the range of about 0.05 microns to about 100microns. The size of the metal particles is typically less than the sizeof the diamond particles. In an embodiment, iron particles may be used.Examples of iron particles that may be used in the process of anembodiment include grade HQ 1 μm carbonyl iron powder (BASF,Ludwigshafen, Germany).

Although iron powder has been mentioned as a powder used in carrying outthe process, other metals such as cobalt, nickel, manganese and chromeand their metal compounds and combinations thereof may be used.

In another embodiment of making modified diamond particles, from about10 to about 80 weight percent diamond particles and from about 20 toabout 90 percent iron particles are mixed using any appropriate mixingmethod that achieves a uniform mixture. In an embodiment, the weighedportions of the iron and diamond particles are put into a jar, sealedand inserted into a mixing device such as a Turbula® shaker-mixer (GlenMills, Inc., Clifton, N.J., U.S.A) for at least about one hour or,alternatively, about 30 minutes to about one hour. A binder mayoptionally be added to the mixture prior to mixing. Binders providelubricity to particle surfaces allowing a denser packing and moreintimate contact between the metal powder and diamond. Binders also helpin holding a pressed body together as a green-body.

The mixture is then compressed so as to create an intimate mixture ofdiamond particles and iron particles. Any method may be used to compressthe diamond particles and iron particles so long that they form anintimate mixture and the particles are in very close contact with oneanother. One method used to compress the mixture is to place the mixtureinto a fixed die set on a press. An example of a suitable press is aCarver® pellet press manufactured by Carver, Inc. (Wabash, Ind.). In thedie press, the mixture is subjected to pressure between about 5 andabout 50,000 psi, between about 10,000 to about 40,000 psi or betweenabout 15,000 to about 30,000 psi to form a pellet. Although pelletizingthe mixture is taught, it is not necessary that the mixture of diamondand iron particles be formed into a pellet, only that the particles becompressed so as to form intimate contact with one another. Isostatic ormonostatic pressing with deformable tooling may also be used to achievethe intimate contact.

Alternatively, the mixture may also be compressed by pressing it into athin sheet that is several millimeters to several inches thick, i.e., byhigh pressure compaction rolls or briquetting rolls. The formed sheetsmay then be cut into smaller sections for further processing asdiscussed below. Another method of compressing the mixture of iron anddiamond particles includes mixing and extruding the mixture underpressure. Pelletizing the mixture of diamond and iron particles via apelletizer or tumbling the mixture in a tumbling apparatus are alsoalternative methods that may be used to compress the mixture. Thepellets, bricks, briquetttes or cakes be formed by these methods maythen be further processed as discussed below

Additional methods of compressing the mixture of iron and diamondparticles include injection molding, extrusion, pressing the mixtureinto a container or tape casting. Alternatively, individual diamondparticles may be coated with metal particles by ion implantation,sputtering, spray drying, electrolytic coating, electroless coating orany other applicable method so long as, the iron and diamond particlesare in intimate contact with each other.

After compressing the mixture of diamond and iron particles, thecompressed mixture, which may be in a pellet, an aggregate or othercondensed form, is placed into a furnace and, in a hydrogen atmosphere,vacuum atmosphere, or an inert gas atmosphere, heated from about 650° C.to about 1000° C. Temperatures of about 700° C. to about 900° C. orabout 750° C. to about 850° C. may be used. The compressed mixture maybe heated for a period of time of from about five minutes up to aboutfive hours. Time periods ranging from about thirty minutes up to abouttwo hours or of about one to about two hours may be used.

After the heating cycle is complete and the compressed mixture iscooled, the modified diamond particles are recovered by dissolving theiron particles in common acids. Acids that may be used includehydrochloric acid, hydrofluoric acids, nitric acid and combinationsthereof. Acids, or combinations thereof, are added in an acid:compressedmixture (i.e., a pellet) ratio of 100:1 up to 1000:1 (by volume). Themixture is then heated between about 100° C. to about 150 C.° for aperiod of from about six to about eight hours. The solution is thencooled, the liberated diamond settles and the solution is decanted. Theacid cleaning and heating steps are repeated until substantially all ofthe iron has been digested.

Subsequently, any converted graphite (carbon from diamond that has beenconverted to graphite during the reaction with iron) is then removedfrom the particles via any dissolution treatment method known in theart. Example of a common dissolution procedure includes the oxidation ofgraphitic carbons by gradual heating range between about 150° C. toabout 180° C. in an acidic solution containing a mixture of HNO₃ andH₂SO₄.

Depending on the furnace conditions chosen, more or less reaction mayoccur between the metal and the diamond. The more the metal powderetches into the diamond, the more graphite is formed and, thus, moreweight is lost by the diamond. To completely dissolve the graphite,higher quantities of acid may be used or additional dissolutiontreatments may be necessary. The diamond particles are then washed toremove acids and residue, such as in water. Subsequently, the diamondparticles are dried in a furnace, air dried, subjected to microwavedrying or other drying methods known in the art.

An embodiment pertains to monocrystalline diamond particles having veryrough, irregular surfaces as shown in FIGS. 9A-9D; FIGS. 10A-10D andFIGS. 11A-11D. In addition to the roughened appearance, the diamondparticles have unique characteristics as compared to conventionalmonocrystalline diamond particles shown in FIG. 12. The conventionalmonocrystalline diamond particles produced by milling, shown in FIG. 12,were not subjected to the modification treatment.

Referring to FIG. 13, Table 2 contains data including sizes, weightloss, surface area, material removal, roughness and sphericity for asample of monocrystalline diamond particles (9 μm). Additionally,comparative data for both a conventional monocrystalline diamondparticle and a conventional polycrystalline diamond particle of similarparticle sizes are shown. This data was used to create the graphs inFIGS. 14 and 15 as discussed below.

As shown in FIGS. 9A-9D; FIGS. 10A-10D and FIGS. 11A-11D, the diamondparticles are very different in appearance compared to conventionalmonocrystalline diamond particles as shown in FIG. 12. FIGS. 9A-9D showSEM images of the diamond particles of Run #4; FIGS. 10A-10D shows SEMimages of the diamond particles of Run#5 and FIGS. 11A-11D show SEMimages of the diamond particles of Run #9. FIG. 13 (Table 2) lists thecorresponding properties and characteristics of the diamond particlesfrom additional samples.

As shown in FIGS. 9A-9D; FIGS. 10A-10D and FIGS. 11A-11D, the diamondparticles include spikes and pits. The spikes act as cutting edges whenused in free-abrasive slurry applications. It has been discovered thatthe performance of the modified diamond particles significantly improveswhen used in free abrasive lapping applications within a liquid slurryor suspension. When the modified diamond particles are used in a fixedbond system, the pits and/or the spikes help secure the particle withinthe bond system.

The modified diamond particles exhibit unique characteristics in surfaceroughness, sphericity and material removal. FIG. 14 shows thesecharacteristics as compared to weight loss of the modified diamondparticles. Details has to how the measurements were obtained arediscussed in Example IV. As shown in FIG. 14, the weight loss of thediamond particles is between greater than 0% to about 70%.

As shown in FIG. 14, diamond particles exhibit a surface roughness ofless than about 0.95. Surface roughness of between about 0.50 and about0.80 and between about 0.50 and about 0.70 is also observed. Surfaceroughness of the diamond particle is a function of the size of the metalparticle(s), amount of metal particle(s) in contact with the diamond,reaction time and temperature used. As can be seen in FIG. 14, as thesurface roughness factor decreases (roughness increases) the ability ofthe diamond to perform material removal in a lapping process (describedin EXAMPLE IV) increases from about 125 mg for a surface roughnessfactor of about 0.92 to about 200 mg for a surface roughness factor ofabout 0.62; an increase of about 60 percent. This may be attributed tothe increased number of cutting points that the surface modificationprovides.

FIG. 14 also shows that the diamond particles also exhibit sphericityreadings of less than about 0.70. Sphericity readings of about 0.2 toabout 0.5 and about 0.25 to 0.4 are also observed. Although sphericityis an independent feature from surface roughness, it can be observedthat there is a strong correlation between sphericity and the lappingperformance of the diamond as shown in FIG. 14. In FIG. 14, it can beshown that the material removal increases from about 125 mg for asphericity of about 0.70 to about 200 mg for a sphericity of about 0.25.Also, as can be seen in FIG. 14, there is a strong correlation betweenthe weight loss of the diamond powder and the lapping performance asindicated by the increase in material (sapphire) removal. As the weightloss of diamond increases, the diamond becomes more aggressive in itsability to remove material.

FIG. 15, is a graph showing diamond weight loss (%) vs. surface area.The readings were taken from a population of 9 μm diamond particles. Thespecific surface area of the modified diamond particles having weightloss greater than 35% is about 20% higher compared to conventionaldiamond particles having the same particle size distribution. It can beobserved that the specific surface area of the particles is directlyproportional to the extent of the reaction of the diamond particles andiron particles during the modification treatment process. For example,specific surface area readings of the diamond particles range from about0.45 to about 0.90 m²/g.

FIGS. 16-19 show examples of various diamond particles that have beensubjected to varying degrees of treatment with iron. FIG. 16 shows adiamond particle that was heated at a temperature of 750° C. for 1 hourin 60% by weight iron resulting in a 15% weight loss of the diamondparticle. FIG. 17 shows a diamond particle that was heated at atemperature of 750° C. for 1 hour in 80% by weight iron resulting in a25% weight loss of the diamond particle. FIG. 18 shows a diamondparticle that was heated at a temperature of 850° C. for 1 hour in 60%by weight iron resulting in a 30% weight loss of the diamond particle.FIG. 19 shows a diamond particle that was heated at a temperature of850° C. for 1 hour in 80% by weight iron resulting in a 45% weight lossof the diamond particle. FIG. 20 shows a diamond particle that washeated at a temperature of 850° C. for 2 hours in 60% by weight ironresulting in a 53% weight loss of the diamond particle. FIG. 21 shows adiamond particle that was heated at a temperature of 850° C. for 2 hoursin 80% by weight iron resulting in a 61% weight loss of the diamondparticle.

The modified diamond particles contain one or more pits and/or spikes.An example of a diamond particle exhibiting these features is shown inFIG. 19. Diamond particle 1, having a weight loss of about 45%, includespits 4,6 that form spike 2. The lengths of the spikes and depths of thepits vary according to the modification treatment parameters. Theaverage depth of the pits on a particle ranges in size from about 5% toabout 70% of the longest length of the particle.

The modified abrasive particles, as described above, may be useful inmany applications including free abrasive applications, fixed abrasiveapplications, lapping, grinding, cutting, polishing, drilling, dicing,sintered abrasives or abrasive compacts, and wire for wire saws. Ingeneral, one would expect that the roughened surface would aid in theretention of the diamond particle within the tool or resin bond system.

With regard to wire saw applications, the abrasive particle may beattached to a wire by electroplating, metal sintering or polymeric orresin bonds. Electroplated wire saws generally contain a single layer ofabrasive particles co-deposited with a layer of nickel metal. Some wiresalso use a resin to attach the abrasives to the wire. The use of themodified diamond particles would aid in providing better retention ofthe abrasive particle in the metal or resin matrix, hence increasing thelife of the wire saw. The modified abrasive particles may also providehigher material removal rate with better free-cutting ability.

Materials typically cut with wire saws include silicon, sapphire, SiC,metals, ceramics, carbon, quartz, stone, glass composites, and granite.

The abrasive particles are also useful in slurries and other carrierliquids. A typical slurry solution may include the modified diamondparticles ranging in size of from about 0.1 to about 100 microns presentin a concentration of about 0.2 to about 50 percent by weight, a majorvehicle such as a water-based vehicle, glycol-based vehicle, oil-basedvehicle or hydrocarbon-based vehicles and combinations thereof andoptional additives including surfactants, pH and color adjusters, andviscosity modifying agents.

In another embodiments, the modified abrasive particles andsuperabrasives may be optionally coated with a coating, aftermodification, such as a material selected from Groups IVA, VA, VIA, Mband IVb of the periodic table and including alloys and combinationsthereof. A non-metallic coating that may be used is silicon carbide.

Example I

A 4-8 μm monocrystalline diamond particles, e.g., diamond powder, with anominal mean size of 6 μm was coated with a nickel/phosphorous coating(90% Ni/10% P). The nickel coated diamond powder contained 30 weightpercent NiP and 70 weight percent diamond. Each diamond particle wasuniformly covered with the NiP coating. Two 25 gram samples of the Nicoated powder were heated in a furnace. One 25 gram sample was heated at825° C. for 1 hour and the other at 900° C. in a hydrogen atmosphere for2 hours. After the heating cycle was completed and the coated diamondpowder was cooled to room temperature, the modified diamond particleswere recovered by dissolving the nickel coated diamond in two liters ofnitric acid. The mixture was then heated to 120 C.° for a period of fivehours. The solution was then cooled to room temperature, the liberateddiamond settled and the solution was decanted. The acid cleaning andheating steps were repeated one additional time until substantially allof the nickel had been digested.

After the nickel was removed from the diamond, the converted graphite(carbon from diamond that has been converted to graphite during thereaction with nickel) was then removed from the particles using 2 litersof sulfuric acid heated to 150° C. for seven hours. The solution wasthen cooled to room temperature, the diamond allowed to settle and thesolution was decanted. The sulfuric acid cleaning and heating steps wererepeated one additional time until substantially all of the graphite hadbeen digested.

Measurements of weight loss, surface roughness and sphericity wereobtained from the material recovered from this experiment. Included inthis analysis was the SJK-5 4-8 μm diamond that was modified using afine iron powder process as described herein. Also included is data fora polycrystalline diamond powder of similar nominal size.

The surface roughness and sphericity were obtained from images of thebase material and modified diamond particles taken with a Hitachi modelS-2600N Scanning Electron Microscope (SEM) at a 2500× magnification. TheSEM images were saved as TIFF image files which were then uploaded intoa Clemex image analyzer Vision PE 3.5 that was calibrated to the samemagnification (2500×). In this example and for this magnification, thecalibration resulted in 0.0446 μm/pixel resolution. The image analysissystem measured particle size and shape parameters on a particle byparticle basis. Measurements for a population of at least 50 particlesfrom each set of experiments were generated automatically by the Clemeximage analyzer. Mathematical formulas used by the image analyzer deviceto derive the measurements are found in the “Definitions” section aboveand can also be found in the Clemex Vision User's Guide PE 3.5 ©2001.Surface characteristics of the diamond particles of the five powdersamples are shown in FIG. 2 (Table 1).

As can be seen from FIG. 1C, the surface texture of the modified diamondparticles produced using the nickel coating method is significantlydifferent than the surface texture of the starting material shown inFIG. 1A. It is apparent that, at temperatures above 800° C., the nickelreacts with the diamond and creates a unique texture that can bedescribed by roughness and sphericity factors using the image analysismethod. Based on the data obtained in this example, the roughness valueschanged from 0.89 to 0.77 for the 35 percent weight loss sample and from0.89 to 0.78 for the 56 percent weight loss diamond. The sphericityvalues changed from 0.64 to 0.47 for the 35 percent weight loss sampleand from 0.64 to 0.46 for the 56 percent weight loss diamond after themodification process.

Note that, as can be seen in FIG. 2 (Table 1), although the modificationprocess at 900° C. results in a higher weight loss of diamond, and aslightly finer size and slightly higher specific surface area comparedto the process performed at 825° C., there is essentially no differencein the roughness and sphericity of these two samples. The surfacetexture produced of the diamond particles can be qualitatively describedas having many small “teeth” or cutting points. Although these featuresare most apparent when looking at the boundary of particle profiles,they also exist across the entire surface of each particle. It isthought that the increase in the number of cutting points, or teeth, isresponsible for the improved performance of the modified diamondparticles. FIG. 6B shows a two-dimensional illustration of the cuttingpoints or teeth of a modified diamond particle. FIG. 6A shows atwo-dimensional illustration of a conventional monocrystalline diamondparticle that has not been modified with a metal coating. FIG. 7 is anSEM image of a conventional monocrystalline diamond particle that hasnot been modified with metal coating. FIG. 8 is an SEM image of showingthe cutting points or teeth of a diamond particle modified with nickelcoating.

For purposes of distinction, the surface texture of the modifiedparticles is different from the texture that was produced using the ironpowder modification process as taught above. As shown in FIG. 1E, theiron powder modified particles display deep pits and spikes. The averageroughness of the iron powder modified diamond is 0.68 and the averagesphericity is 0.34. As shown in FIGS. 3 and 4, these values aresignificantly different than the values measured for the nickel-coatedmodified diamond particles. It can also be seen that, although theparticles modified by iron powder do not have as many cutting points perunit length of perimeter as the nickel coated modified diamond, thedeeper pits and pockets could be useful in providing better retentionwithin a bond system.

Example II

A MBG-620 70/80 mesh monocrystalline diamond particles was coated with anickel/phosphorous coating (90% Ni/10% P). The nickel coated diamondpowder contained 56 weight percent NiP and 44 weight percent diamond.Each diamond particle was uniformly covered with the NiP coating. 5grams sample of the Ni coated powder were heated in a furnace at 1000°C. for 1 and half hour under hydrogen environment. After the heatingcycle was completed and the coated diamond powder was cooled to roomtemperature, the modified diamond particles were recovered by dissolvingthe nickel coated diamond in 500 ml of nitric acid. The mixture was thenheated to 120 C.° for a period of five hours. The solution was thencooled to room temperature, the liberated diamond settled and thesolution was decanted. The acid cleaning and heating steps were repeatedone additional time until substantially all of the nickel had beendigested.

After the nickel was removed from the diamond, the converted graphitewas then removed from the particles using 500 ml of sulfuric acid and100 ml nitric acid and heated to 150° C. for seven hours. The solutionwas then cooled to room temperature, the diamond allowed to settle andthe solution was decanted. The sulfuric acid cleaning and heating stepswere repeated one additional time until substantially all of thegraphite had been digested.

A 14% diamond weight loss has been achieved with this experiment.Samples of the particles are shown in FIGS. 27A and 27B.

Example III

The diamond powders of Example 1 were additionally evaluated in asapphire lapping application. Ethylene glycol-based slurries were madeusing the monocrystalline modified diamond particles (“Nickel CoatingModified Diamond”) and, from the same lot, conventional monocrystallinediamond particles “(Unmodified Diamond”) from which the nickel coatingmodified diamond was made. Slurries were also made from iron powdermodified diamond as described in Example 1 as well as from conventionalpolycrystalline diamond. The slurries were used for flat-lappingsapphire wafers. The lapping plate was a composite copper/resin material(Lapmaster Inc.) and the sapphire wafers were c-plane, 2 inchesdiameter, as-lapped surface texture and 490 μm thick. The lappingprocess was performed using each of the slurries under the sameprocessing conditions and for the same amount of time. The diamondconcentration in each of the slurries was 10 carats per 500 ml and theviscosity was 15-20 cps. Before each test, the lapping plate was dressedfor 5 minutes using a 600 grit diamond dressing wheel. The pressure oneach of the sapphire wafers was 3.2 psi, rotational speed of the lappingplate was 60 rpm and the slurry feed rate was 2-3 ml per minute. Aftereach cycle, the wafers were measured for weight loss.

FIG. 5 is a graph comparing the lapping performance of conventional 4-8micron monocrystalline diamond particles in a slurry with 10 carats ofdiamond in 500 ml slurry, conventional 4-8 micron polycrystallinediamond particles in a slurry with 10 carats of diamond in 500 ml slurryand two slurries using modified 4-8 micron monocrystalline diamondparticles of 35 percent weight loss and 56 percent weight loss using 10carats of diamond per 500 ml of slurry. As can be seen from FIG. 5 andin FIG. 2 (Table 1), the material removal rate of the conventional 4-8μm diamond slurry is 126 mg per hour per sapphire wafer. Using theslurry made with the polycrystalline diamond particles, the materialremoval rate was 168 mg/hr. The slurries made using the modified diamondparticles resulted in material removal rates of 279 mg/hr for the 35percent weight loss powder and 304 mg/hr using the 56 percent weightloss powder.

It can also be seen from the results shown in FIG. 5 that, although themodified diamond particles provide significantly higher material removalrates, the resulting roughness (R_(a)) of the surface of the sapphirewafers are lower than with the conventional monocrystalline diamond andwith the polycrystalline diamond. The wafer roughness of wafers polishedwith the polycrystalline diamond slurry was 45.9 nm+/−3.5 nm and thewafer roughness of wafers polished with the monocrystalline diamond was51.3 nm+/−2.7 nm. By comparison, the wafer roughness of the sapphirewafers polished using the 35 percent weight loss diamond was 32.8nm+/−1.8 nm and wafers polished with the 56 percent weight loss diamondslurry had a wafer roughness of 33.7 nm+/−2.7 nm as measured by a VeecoWyco Model NT1100 Optical Surface Profilometer.

As shown in FIG. 2 (Table 1) it can be seen that the specific surfaceareas of the monocrystalline modified diamond particles are 1.29 m²/gramand 1.55 m²/gram for a 35 percent and 56 percent weight loss diamondrespectively. This compares to a specific surface area of 0.88 m²/gramor a 47% and 76% increase. This is significant because the particle sizedistributions of the two samples are the same. The increased surfacearea is due to the creation of additional area on the surface of themodified monocrystalline diamond particles.

Example Iv

A 6-12 μm monocrystalline diamond powder with a mean size of 9 μm wasblended with an iron powder with a mean size of 3 μm using a blend ratioof 30 weight percent diamond particles and 70 weight percent iron powder(no binder). The blend was compacted into a 2 cm×0.5 cm pellet using aCarver press at a pressure of 20,000 psi. The pellet was heated at 700°C. for 2 hours in a hydrogen atmosphere. The diamond particles wererecovered using an acid digestion process. Characteristics of thediamond particles of this sample are shown in FIG. 13 (Table 2).

Ethylene glycol-based slurries were made using the monocrystallinediamond particles of the present invention (“Modified Diamond”) and,from the same lot, conventional monocrystalline diamond particles“(Unmodified Diamond”) from which the modified diamond was made. Theslurries were used for flat-lapping sapphire wafers. The lapping platewas a composite copper plate and the sapphire wafers were 2 inches indiameter. The lapping process was performed using each slurry under thesame processing conditions and for the same amount of time. The slurrydiamond concentration was 10 carats per 500 ml and the viscosity was15-20 cps. Before each test, the lapping plate was dressed for 5 minutesusing a 600 grit diamond dressing wheel. The pressure on each of thesapphire wafers was 3.2 psi, rotational speed of the lapping plate was60 rpm and the slurry feed rate was 2-3 ml per minute. After each cycle,the wafers were measured for weight loss.

FIG. 22 is a graph comparing the lapping performance of conventional6-12 micron monocrystalline diamond particles in a slurry with 10 caratsof diamond in 500 ml slurry, conventional 8-12 micron polycrystallinediamond particles in a slurry with 10 carats of diamond in 500 ml slurryand 6-12 micron monocrystalline diamond particles (Modified 6-12) inslurries using 10 carats of diamond of the present invention per 500 mlof slurry and a slurry using 20 carats of diamond of the presentinvention per 500 ml of slurry.

It has been shown that the increase in specific surface areas of themonocrystalline diamond particles of the present invention (“ModifiedDiamond”) compared to the conventional monocrystalline diamond particles(“Unmodified Diamond”) is 0.64 m²/gram vs. 0.50 m²/gram or a 28%increase. This is significant because the particle size distributions ofthe two samples are the same. The increased surface area is due to thecreation of additional area on the surface of the monocrystallinediamond particles of the present invention.

Example V

A series of seven additional experiments were performed whereby samplesof 9 μm conventional monocrystalline diamond particles and iron powderwere pressed into pellets (according to Example III) using various timesand temperatures, as indicated in FIG. 23, Table 3.

The diamonds were processed and recovered as described in Example IV.Measurements of weight loss, surface roughness and sphericity wereobtained from the samples recovered from these experiments.Additionally, slurries were made from each of the samples and tested inthe lapping test also described in Example IV.

For each sample, images of the modified diamond particles were takenwith a Hitachi model S-2600N Scanning Electron Microscope (SEM) at a2500× magnification. The SEM images were saved as TIFF image files whichwere then loaded into a Clemex image analyzer Vision PE 3.5 that wascalibrated to the same magnification (2500×). In this example and forthis magnification, the calibration resulted in 0.0446 μm/pixelresolution. The image analysis system measured particle size and shapeparameters on a particle by particle basis. Measurements for apopulation of at least 50 particles from each set of experiments weregenerated automatically by the Clemex image analyzer. Mathematicalformulas used by the image analyzer device to derive the measurementsare found in the “Definitions” section above and can also be found inthe Clemex Vision User's Guide PE 3.5 ©2001. Surface roughness andsphericity were calculated and are reported in FIG. 13 (Table 2) inaddition to weight loss and specific surface area for each test. Resultsfrom Example IV are also included in FIG. 13 (Table 2).

Equivalents

Although the invention has been described in connection with certainexemplary embodiments, it will be evident to those of ordinary skill inthe art that many alternatives, modifications, and variations may bemade to the disclosed invention in a manner consistent with the detaileddescription provided above. Also, it will be apparent to those ofordinary skill in the art that certain aspects of the various disclosedexample embodiments could be used in combination with aspects of any ofthe other disclosed embodiments or their alternatives to produceadditional, but not herein explicitly described, embodimentsincorporating the claimed invention but more closely adapted for anintended use or performance requirements. Accordingly, it is intendedthat all such alternatives, modifications and variations that fallwithin the spirit of the invention are encompassed within the scope ofthe appended claims.

The invention claimed is:
 1. A monocrystalline diamond particle havingan irregular surface, wherein the surface roughness of said particle isless than about 0.95, said particle including one or more spikes and oneor more pits, wherein a depth of the one or more pits ranges in sizefrom about 5% to about 70% of a longest length of the particle.
 2. Theparticle of claim 1, wherein the surface roughness of said particle isbetween about 0.50 and about 0.80.
 3. The particle of claim 1, whereinthe sphericity of said particle is less than about 0.70.
 4. The particleof claim 3, wherein the sphericity of said particle is between about0.25 to about 0.6.
 5. The particle of claim 1, where the size of theparticle is between about 0.1 to about 1000 microns.
 6. The particle ofclaim 1, wherein the depth of the pits ranges in size from about 40% toabout 60% of the longest length of the particle.
 7. The particle ofclaim 1, wherein said particle comprises a metallic coating.
 8. Theparticle of claim 1, wherein in said particle ranges in size from about0.1 micron to about 1000 microns.
 9. A monocrystalline diamond particlehaving a sphericity of less than about 0.70, said particle including oneor more spikes and one or more pits, wherein a depth of the one or morepits ranges in size from about 5% to about 70% of a longest length ofthe particle.
 10. The particle of claim 9, wherein the sphericity ofsaid particle is about 0.2 to about 0.5.
 11. The particle of claim 9,wherein the sphericity of said particle is about 0.25 to 0.4.
 12. Amonocrystalline diamond particle having an irregular surface, whereinthe surface roughness of said particle is less than about 0.70, saidparticle including one or more spikes and one or more pits.
 13. Amonocrystalline diamond particle of claim 12, having an irregularsurface, wherein the surface roughness of said particle is less thanabout 0.60.